Distal Tip Assembly for a Heart Valve Delivery Catheter

ABSTRACT

A catheter assembly according to the present invention includes a handle assembly, an introducer sheath, and a distal tip assembly. The distal tip assembly can include first and second retaining sleeves and a slotted tip with a non-traumatic tip guard positioned at the proximal end of the slotted tip. The handle assembly can include a fixed main handle and two or more rotating handles that allow a user to control the distal tip assembly of the catheter. Each control knob on the handle assembly controls a portion of the components on the distal by of the catheter by allowing for precise manipulation of various delivery shafts. Each delivery shaft extends from the handle assembly to respective positions towards the distal end of the catheter.

BACKGROUND

1. Field

The present invention relates to catheters for delivering a prosthesisand, particularly, to delivery catheters having an a traumatic distaltip assembly.

2. Background

Recently, minimally invasive approaches have been developed tofacilitate catheter-based implantation of prostheses, for example,transcatheter aortic-valve prosthesis implantation. Typically, duringtranscatheter prosthesis implantations, a prosthesis is radiallycontracted onto a delivery catheter so that the prosthesis can beintroduced into a body lumen, for example, into the femoral artery, thebrachial artery, or the aorta, or into a body cavity, for example, achamber of the heart (e.g., the ventricle). The contracted configurationof the prosthesis on the delivery catheter can be maintained by aretaining sleeve positioned over the prosthesis. Using the deliverycatheter, the prosthesis can then be guided to the desired implantationsite through the body lumen or body cavity. Once the prosthesis isadvanced to a desired target site, the prosthesis can be deployed byremoving the retaining sleeve and allowing the prosthesis to expand, forexample, through balloon expansion or self-expansion.

A delivery catheter sometimes must be navigated through the tortuousanatomy of a body lumen or cavity. As the catheter articulates throughthe tortuous anatomy, the retaining sleeve can bend. The bending actionof the retaining sleeve can cause the distal, leading edge of theretaining sleeve to flex outward (e.g., “fishmouth”) from an adjacentdistal tip of the delivery catheter, exposing the distal edge. Theexposed edge of the retaining sleeve can contact the wall of the bodylumen or cavity, which can cause damage to the wall, especially indiseased body lumens. For example, during a trans-femoral delivery of aheart valve prosthesis, the delivery catheter must navigate around theaortic arch, which can cause the retaining sleeve to bend and can exposethe retaining sleeve's distal, leading edge. The exposed leading edge ofthe retaining sleeve may damage the aortic wall if the edge contacts thewall.

Accordingly, there is a need for delivery catheters that have anatraumatic distal tip assembly that can reduce the risk of damage to thewalls of the body lumen or cavity that may occur during delivery of aprosthesis to a desired target site.

BRIEF SUMMARY

A catheter for implanting a prosthesis can include a retaining sleevethat defines a hollow cavity. The retaining sleeve can contain aprosthesis. The retaining sleeve has an outer diameter. The catheter canalso have a distal tip assembly configured to move axially relative tothe retaining sleeve. The distal tip assembly can have a distal portionand a proximal portion. The proximal portion can be configured to movebetween a contracted position having a first outer diameter and anexpanded position having a second outer diameter. The second outerdiameter being larger than the outer diameter of the retaining sleeve.

A method of implanting a prosthesis can include inserting a retainingsleeve and a distal tip assembly of a catheter assembly into a bodylumen. The retaining sleeve can be positioned over the prosthesis. Theretaining sleeve has an outer diameter. The distal tip assembly can havea distal portion and a proximal portion. The method can also includeexpanding the outer diameter of the proximal portion of the distal tipassembly such that the outer diameter of the proximal portion is largerthan the outer diameter of the retaining sleeve.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying drawings, which are incorporated herein and form partof the specification, illustrate the present invention and, togetherwith the description, further serve to explain the principles of theinvention and to enable a person skilled in the relevant art(s) to makeand use the invention.

FIG. 1 illustrates a delivery catheter according to an embodiment.

FIG. 2 illustrates a distal tip assembly and a retaining sleeve of adelivery catheter according to an embodiment.

FIG. 3 illustrates a cross-sectional view of the distal tip assembly andthe retaining sleeve of FIG. 2 according to an embodiment.

FIG. 4 illustrates a distal tip assembly and an introducer of a deliverycatheter according to an embodiment.

FIG. 5 illustrates a cross-sectional view of the distal tip assembly andthe introducer of FIG. 4 according to an embodiment.

FIG. 6 illustrates the distal tip assembly and the introducer of FIGS. 4and 5 according to an embodiment.

FIG. 7 illustrates a biasing member according to an embodiment.

FIG. 8 illustrates a cross-sectional view of the biasing member of FIG.7 and a distal tip assembly of a delivery catheter according to anembodiment.

FIG. 9 illustrates a cross-sectional view of a distal tip assemblyaccording to an embodiment.

FIG. 10 illustrates an enlarged cross-sectional view of the distal tipassembly of FIG. 9.

FIG. 11 illustrates a cross-sectional view of a distal tip assemblyhaving a biasing member according to an embodiment.

FIG. 12 illustrates the distal tip assembly and the biasing member ofFIG. 11 according to an embodiment.

FIG. 13 illustrates the distal tip assembly and the biasing member ofFIGS. 11 and 12 according to an embodiment.

DETAILED DESCRIPTION

The following description of prosthesis delivery catheters and methodsof delivering and implanting a prosthesis refers to the accompanyingfigures that illustrate exemplary embodiments. Other embodiments arepossible. Modifications can be made to the embodiments described hereinwithout departing from the spirit and scope of the present invention.Therefore, the following detailed description is not meant to belimiting. Further, it would be apparent to one of skill in the art thatthe systems and methods described below can be implemented in manydifferent embodiments of hardware. Any actual hardware described is notmeant to be limiting. The operation and behavior of the systems andmethods presented are described with the understanding thatmodifications and variations of the embodiments are possible given thelevel of detail presented. For example, the delivery catheter describedbelow can be adapted for use with different types of prostheses, forexample, heart valve prostheses, stents, or valves prostheses for areasof the body other than the heart, and for different approaches, forexample, transapical, subclavian, brachial, or trans-femoral. One ofskill in the art would readily understand how to incorporate thefeatures and structures described herein into catheters intended forother purposes.

FIG. 1 illustrates a catheter assembly 100 according to an embodiment.Catheter assembly 100 generally includes a handle assembly 102 locatedat the proximal end of the catheter, a distal tip assembly 104 locatedat the distal end of the catheter, and an introducer 116 slidablylocated along an outer delivery shaft 106 extending from handle assembly102. Outer delivery shaft 106 can be tubular. Outer delivery shaft 106can be formed of braided material fabricated from, for example,polyethylene naphthalate (PEN), polyester (PET), stainless steel,titanium, nitinol, cobalt nickel alloy, polyamide, polyimide, or thelike. In some embodiments, outer delivery shaft 106 can have a degree offlexibility, for example, outer delivery shaft 106 is capable ofarticulating around a bend in a body lumen while still having sufficientaxial strength to prevent buckling during delivery. Other suitableflexible materials can also be used to form outer delivery shaft 106 inother embodiments.

Handle assembly 102 can include a main handle 108, a proximal controlknob 110, and a distal control knob 112. Main handle 108, a proximalcontrol knob 110, and distal control knob 112 can be formed of anysuitable material. For example, in some embodiments the handle andcontrol knobs are formed of a polymer material. Other materials arepossible, as would be understood in the art it is understood that thehandle and control knob, for example, need not be made of the samematerial.

Handle assembly 102 can include a flushing port 114 on main handle 108.Flushing port 114 can, for example, be used to de-air the catheterassembly, to introduce fluid into the native annulus to preventcoagulation and/or thrombosis, to deliver site specific drugs, or tointroduce radiopaque fluid into the body.

Catheter assembly 100 can include a flushing tap 118 and a flushing taplead 120 connected to introducer 116. Introducer 116 can be a tubularmember that is slidably located over outer delivery shaft 106.Introducer 116 can be formed of a variety of materials, for example,stainless steel or various polymer materials.

Catheter assembly 100 further includes a prosthesis retaining sleeve 130and a prosthesis retaining sleeve connector 134. Prosthesis retainingsleeve 130 can be a tubular cylinder that defines a hollow cavityconfigured to receive a contracted prosthesis, for example, a heartvalve prosthesis. Accordingly, prosthesis retaining sleeve 130 maintainsthe contracted configuration of the prosthesis on the delivery catheterassembly 100. Prosthesis retaining sleeve connector 134 securesprosthesis retaining sleeve 130 to the distal end of outer deliveryshaft 106. Outer delivery shaft 106 extends distally from the interiorof handle assembly 102 to sleeve connector 134.

Proximal control knob 110 and distal control knob 112 can be manipulatedby a user to control operation of distal tip assembly 104, a prosthesisretaining sleeve 130, or both. In one embodiment, prosthesis retainingsleeve 130 and distal tip assembly 104 are configured to move axiallyrelative to each other. For example, prosthesis retaining sleeve 130connected to delivery shaft 106 can be advanced proximally, whilekeeping distal tip assembly 104 stationary, such that prosthesisretaining sleeve 130 moves away from distal tip assembly 104 to an openconfiguration as shown in FIG. 1. Prosthesis retaining sleeve 130 can beadvanced distally, while keeping distal tip assembly 104 stationary,such that the prosthesis retaining sleeve 130 moves towards distal tipassembly 104 until the distal edge of retaining sleeve 130 is adjacentand, in some embodiments, abuts distal tip assembly 104 to a closedconfiguration (as shown in FIG. 2). Alternatively or conjunctively,distal tip assembly 104 can be configured to move axially in theproximal and distal directions. Accordingly, to move catheter assembly100 into the open configuration as shown in FIG. 1, distal tip assembly104 and intermediate delivery shaft 132 to which distal tip assembly 104is attached can be advanced distally while keeping retaining sleeve 130stationary. To move catheter assembly 100 into the closed position,distal tip assembly 104 and intermediate delivery shaft 132 can beadvanced proximally towards prosthesis retaining sleeve 130.

Distal tip assembly 104 is positioned on and connected to the distal endof intermediate delivery shaft 132. Intermediate delivery shaft 132extends from the interior of handle assembly 102 to distal tip assembly104, to which the distal end of intermediate deliver shaft 132 isattached. Intermediate delivery shaft 132 is encompassed by outerdelivery shaft 106 from the interior of handle assembly 102 until outerdelivery shaft 106 terminates at sleeve connector 134.

Intermediate delivery shaft 132 can be a tubular member, in oneembodiment, a guide wire shaft 138 (see, e.g., FIGS. 3 and 8-11) isencompassed within intermediate delivery shaft 132 and extends from theinside of handle assembly 102 to the distal end of distal tip assembly104. Accordingly, catheter 100 can be configured to be advanced along aguide wire (not shown), for example, a guide wire having a 0.035 inchdiameter. However, the dimensions of the catheter components can beadjusted for advancement over guide wires with larger or smallerdiameters.

In one embodiment, at least three shafts (for example, delivery shaft106, intermediate shaft 132, and guide wire shaft 138) extend fromhandle assembly 102, and the shafts are nested along at least a part oftheir lengths. Guide wire shaft 138 is encompassed by intermediatedelivery shaft 132 from a position inside of handle assembly 102 to aproximal portion 124 of distal tip assembly 104, which can be hollowthrough at least a portion thereof. Intermediate delivery shaft 132 isconnected to, and ends at, proximal portion 124 of distal tip assembly104. In turn, intermediate delivery shaft 132 is encompassed by outerdelivery shaft 106 from a position inside handle assembly 102 to theprosthesis retaining sleeve connector 134. Outer delivery shaft 106 isconnected to, and ends at, the retaining sleeve connector 134.Intermediate delivery shaft 132 and guide wire shaft 138 can beconstructed of various polymer materials. Persons of ordinary skill inthe art would appreciate that the lengths and configurations ofintroducer 116, delivery shaft 106, intermediate delivery shaft 132, andguide wire shaft 138 can be modified depending on the application.

In one embodiment, distal tip assembly 104 includes a distal portion 122and proximal portion 124. Distal portion 122 can have any suitableatraumatic shape, for example, a shape that does not have any bluntedges. Atraumatic shapes can include, for example, a semi-sphericalshape, a conical shape with a rounded distal tip (as illustrated inFIGS. 1-13), or any other suitable atraumatic shapes. Distal portion 122can be made of any suitable flexible material, for example, a polymermaterial, to prevent trauma to the wall of a body lumen or cavity.Distal portion 122 can function as a solid dilator tip, in oneembodiment, distal portion 122 cannot expand the outer diameter does notchange.

Proximal portion 124 can be configured to move from a contractedposition to an expanded position having a larger outer diameter.Proximal portion 124 can have an outer diameter in the expanded positionthat is larger than an outer diameter of prosthesis retaining sleeve130. In one embodiment, the outer diameter of proximal portion 124 islarger than the outer diameter of retaining sleeve 130 at its distaledge. In the expanded position, proximal portion 124 can have anysuitable profile, for example, an arcuate profile (in which the largestouter diameter occurs at a central portion of proximal portion 124), astraight profile (in which the outer diameter is constant along theentire length of proximal portion 124), or a tapered profile (in whichthe outer diameter increases as proximal portion 124 extends proximally,for example, such that a proximal end of proximal portion 124 has thelargest outer diameter).

FIG. 2 illustrates a distal tip assembly 104 and retaining sleeve 130according to an embodiment. Retaining sleeve 130 is positioned overprosthesis 200, for example, a heart valve prosthesis. Proximal portion124 is in a contracted position such that the outer diameter of proximalportion 124 is substantially the same as the outer diameter ofprosthesis retaining sleeve 130. Proximal portion 124 can include aballoon element 126. Balloon element 126 can be a flexible membercapable of containing a fluid, for example, air or water. Balloonelement 126 can be inflated by a change in pressure and, particularly,an increase of pressure on an interior side of balloon element 126.Balloon element 126 can encircle the outer contour of proximal portion124. As shown in FIG. 2, distal tip assembly 104 and retaining sleeve130 are in the closed configuration in which proximal portion 124 isadjacent and, in some embodiments, abuts prosthesis retaining sleeve130.

FIG. 3 illustrates distal tip assembly 104 with proximal portion 124 inan expanded position according to an embodiment. Distal tip assembly 104and retaining sleeve 130 are in the closed configuration such thatproximal portion 124 is adjacent to the distal, leading edge ofretaining sleeve 130. Proximal portion 124 is in an expanded positionsuch that the outer diameter of proximal portion 124 is larger than theouter diameter of valve retaining sleeve 130. As shown in FIG. 3,proximal portion 124 has an arcuate outer profile. In this position, theenlarged outer diameter of proximal portion 124 provides an atraumaticcushion for the distal edge of retaining sleeve 130 should it flareoutward during delivery, for example, while navigating a tortuous bendin a body lumen or cavity. The proximal portion 124 would contact thewall before the edge of retaining sleeve 130 and deflect distal tipassembly 104 and retaining sleeve 130 away from the wall.

Proximal portion 124 includes balloon element 126. Balloon element 126forms a seal with interior portion 142 and/or distal portion 122 to formouter cavity 140 for receiving a fluid, for example, air or water.

In one embodiment, proximal portion 124 can also include an interiorportion 142 that extends proximally from distal portion 122. Interiorportion 142 can be cylindrical and can define a center cavity 144.Center cavity 144 can be sized and configured to closely receiveintermediate shaft 132, forming a fluid seal. Interior portion 142 candefine an aperture 146 in communication with cavity 140 and centercavity 144. Guide wire shaft 138 can be sized and configured such thatits outer diameter is spaced apart from the inner diameter ofintermediate shaft 132. The gap between guide wire shaft 138 andintermediate shaft 132 can be used as a fluid passage for transferringfluid to or from cavity 140 to change the pressure and, thus, expand orcontract balloon element 126.

FIG. 4 illustrates distal tip assembly 104 and introducer 116 accordingto an embodiment. Distal tip assembly 104, including proximal portion124, is within introducer 116. Proximal portion 124 can include abiasing member 152 (see FIG. 5). Biasing member 152 can bias proximalportion 124 outward against introducer 116. In this embodiment,introducer 116 prevents the outer diameter of proximal portion 124 frombeing significantly greater, if at all, than the outer diameter ofretaining sleeve 130.

FIG. 5 is a cross-sectional view of distal tip assembly 104 according toan embodiment. Proximal portion 124 includes an annular flange 128 thatextends proximally from the proximal end of distal portion 122. Annularflange 128 can be flexible, for example, annular flange 128 is capableof bending radially inward or outward with the application of a force.Annular flange 128 can define a chamber 150. Chamber 150 can encircleinterior portion 142 of proximal portion 124. Chamber 150 can beconfigured and arranged to receive biasing member 152. Biasing member152 has at least one outwardly biased member. In some embodiments,biasing member 152 has more than one outwardly biased member. Whenseated within chamber 150, biasing member 152 applies an outward forceagainst annular flange 128, biasing annular flange 128 outward againstintroducer 116. When proximal portion 124 is within introducer 116,proximal portion 124 is in a contracted position with its outer diametersubstantially the same as the outer diameter of retaining sleeve 130. Insome embodiments (not shown in FIG. 5), annular flange 128 connects withthe proximal end of interior support 112 to completely surround biasingmember 152.

FIG. 6 illustrates distal tip assembly 104, retaining sleeve 130, andintroducer 116 according to an embodiment. The outward biased member(s)of biasing member 152 (not shown) apply an outward force to annularflange 128 (not shown). Accordingly, when proximal portion 124 extendspast introducer 116, biasing member 152 causes proximal portion 124 toexpand such that its outer diameter is larger than the outer diameter ofretaining sleeve 130.

FIG. 7 depicts biasing member 152 according to an embodiment. Biasingmember 152 can be a spring. In one embodiment, biasing member 152includes a pair of annular rings 154. The outwardly biased member(s) ofbiasing member 152 can include a plurality of spaced apart leaflets 156running between the pairs of annular rings 154. Leaflets 156 are biasedoutward, for example, the center portions of leaflets 156 arc radiallyoutward from annular rings 154. In one embodiment, biasing member 152can be made of any suitable shape memory material, for example, nitinol.The shape memory material can create the outward bias of leaflets 156 ata certain temperatures, for example, the temperature of blood within thebody. In some embodiments, biasing member 152 can be made from othersuitable materials, for example, any suitable metal or plastic. In otherembodiments, leaflets 156 can have stress concentrations that create theoutward bias of biasing member 152.

FIG. 8 depicts a cross-sectional view of distal tip assembly 104including biasing member 152 as shown in FIG. 7 according to anembodiment. Biasing member 152 is seated within chamber 150 defined byannular flange 128. As shown in FIG. 8, proximal portion 124 is in anexpanded position having an outer diameter greater than the outerdiameter of retaining sleeve 130. Proximal portion 124 is adjacent theretaining sleeve 130. Accordingly, the larger diameter of proximalportion 124 provides an atraumatic cushion for the distal edge ofretaining sleeve 130 during delivery.

In some embodiments, as shown in FIGS. 5 and 8, biasing member 152 iscoupled directly to only interior portion 142 extending proximally fromdistal portion 122. For example, both annular rings 154 of biasingmember 152 are adjacent interior portion 142.

In other embodiments, for example, as shown in FIGS. 9 and 10 thatillustrate cross-sectional views of distal tip assembly 104 according toan embodiment, a proximal portion of biasing member 152 is coupleddirectly to intermediate shaft 132, and a distal portion of biasingmember 152 is coupled to distal portion 122 and/or interior portion 142.For example, the proximal annular ring 154 is adjacent intermediateshaft 132, and the distal annular ring 154 is adjacent interior portion142 extending proximally from distal portion 122. Accordingly, addingcompression or tension to intermediate shaft 132 can control movement ofbiasing member 152. Particularly, as intermediate shaft 132 is advanceddistally relative to distal portion 122 and interior portion 142, theproximal annular ring 154 attached to intermediate shaft 132 movesdistally, causing leaflets 156 to deflect radially outward because thedistal annular ring 154 remains stationary relative to distal portion122 and interior portion 142. As intermediate shaft 132 is advancedproximally relative to distal portion 122 and interior portion 142, theproximal annular ring 154 attached to intermediate shaft 132 movesproximally, causing leaflets 156 to flatten because the distal annularring 154 remains stationary relative to distal portion 122 and interiorportion 142.

FIG. 11 is a cross-sectional view of distal tip assembly 104 andretaining sleeve 130 according to an embodiment. As shown in FIG. 11,the profile of proximal portion 124 in the expanded position is taperedwith the outer diameter of proximal portion 124 increasing as proximalportion 124 extends proximally. Thus, the proximal edge of proximalportion 124 has the largest outer diameter. Annular flange 128, and insome embodiments a portion of distal portion 122, can have anover-molded biasing member 152—biasing member 152 is encased by proximalportion 124. Biasing member 152 can having one or more outwardly biasedmembers that cause annular flange 128 of proximal portion 124 to flareradially outward, giving proximal portion 124 a larger diameter than theouter diameter of retaining sleeve 130.

FIGS. 12 and 13 illustrate proximal portion 124 in a contracted positionand in an expanded position, respectively, according to an embodiment.Biasing member 152 includes annular ring 158 and a plurality of spacedapart tabs 160 that extend proximally from annular ring 158. Tabs 160are biased outward, causing flange 128 to flare outward as seen in FIG.13. Annular ring 158 can be over-molded within proximal portion 124 orboth the proximal portion 124 and distal portion 122.

In another embodiment (not shown), annular flange 128 can have apreformed profile having an outer diameter of proximal portion 124 thatis larger than the outer diameter of retaining sleeve 130. Accordingly,annular flange 128 can be in the expanded position without biasingmember 152.

A method of implanting a prosthesis, for example, a heart valveprosthesis, using a catheter according to an embodiment includesinserting distal tip assembly 104 into a body lumen or cavity, forexample, the femoral artery, the aorta, the subclavian artery, thebrachial artery, or into a chamber of the heart, for example, theventricle via a patient's heart apex, as is known in the art. Oncewithin the body lumen or cavity, the proximal portion 124 can beexpanded to the expanded position having an outer diameter greater thanthe outer diameter of retaining sleeve 130. The expanded position ofproximal portion 124 creates an atraumatic cushion between the wall ofthe body lumen and the distal edge of retaining sleeve 130. In theexpanded condition, proximal portion 124 will contact the wall of thebody lumen or cavity before the distal, leading edge of retaining sleeve130, which will deflect the leading edge of the retaining sleeve awayfrom the wall. In one embodiment, the proximal portion 124 assumes theexpanded position automatically once distal tip assembly 104 passesthrough introducer 116, for example, when proximal portion 124 includesbiasing member 152. In another embodiment, proximal portion 124 isselectively expanded to the expanded position, for example, byincreasing the pressure in cavity 140 defined by balloon element 126, orin another embodiment by applying compression or tension to intermediateshaft 132 that is connected to a proximal portion of biasing member 152,deflecting biasing member 152.

After expanding proximal portion 124, distal tip assembly 104 can beadvanced to a desired target site. The atraumatic cushion created by theproximal portion 124 in the expanded position reduces the risk of damageto the walls of the body lumen or cavity during advancement,particularly, advancement through a bend. At the target site, prosthesis200, for example, a heart valve prosthesis, is released from thedelivery catheter 100, for example, by moving distal tip assembly 104and retaining sleeve 130 to the open configuration. In some embodiments,a user rotates the knobs of handle assembly 102 to move distal tipassembly 104 distally relative to retaining sleeve 130 to releaseprosthesis 200. Prosthesis 200 can then expand against the body lumen orcavity wall to secure prosthesis 200 in place.

After deployment of prosthesis 200, distal tip assembly 104 andintroducer 116 can be removed from the body lumen or cavity. In oneembodiment, proximal portion 124 is selectively reduced to thecontracted position. For example, proximal portion 124 can beselectively reduced by decreasing the pressure within cavity 140 definedby balloon element 126, or by deflecting biasing member 152 through theapplication of compression or tension to intermediate shaft 132 attachedto biasing member 152. Distal tip assembly 104 is then pulled backthrough prosthesis 200. Distal tip assembly 104 can be withdrawn intointroducer 116. The introducer 116 and distal tip assembly 104 are thenwithdrawn from the body lumen or cavity. In another embodiment, proximalportion 124 is reduced to the contracted position when proximal portionis pulled back through introducer 116.

In some embodiments, prosthesis 200 can be a heart valve prosthesisdelivered, for example, through a transapical approach, a subclavianapproach, a transfemoral approach, and a brachial approach. Componentsand methods according to embodiments of the present invention can beused in conjunction with catheters designed for alternate approaches.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the invention that others can, by applyingknowledge within the skill of the art, readily modify and/or adapt forvarious applications such specific embodiments, without undueexperimentation, without departing from the general concept of thepresent invention. Therefore, such adaptations and modifications areintended to be within the meaning and range of equivalents of thedisclosed embodiments, based on the teaching and guidance presentedherein.

It is to be understood that the phraseology or terminology herein is forthe purpose of description and not of limitation, such that theterminology or phraseology of the present specification is to beinterpreted by the skilled artisan in light of the teachings andguidance. The breadth and scope of the present invention should not belimited by any of the above-described exemplary embodiments, but shouldbe defined only in accordance with the following claims and theirequivalents.

What is claimed is:
 1. A catheter for implanting a prosthesis,comprising: a retaining sleeve defining a hollow cavity for containing aprosthesis, the retaining sleeve having an outer diameter; and a distaltip assembly configured to move axially relative to the retainingsleeve; the distal tip assembly having: a distal portion, and a proximalportion configured to move between a contracted position having a firstouter diameter to an expanded position having a second outer diameter,the second outer diameter being larger than the outer diameter of theretaining sleeve.
 2. The catheter of claim 1, wherein the proximalportion comprises a balloon element.
 3. The catheter of claim 1, whereinthe proximal portion further comprises an interior portion extendingproximally from the distal portion, and wherein the balloon elementforms a seal with the inner portion.
 4. The catheter of claim 1, whereinthe proximal portion comprises a biasing member.
 5. The catheter ofclaim 4, wherein the biasing member is a spring.
 6. The catheter ofclaim 5, wherein the proximal portion includes an annular flangeextending proximally from the distal portion, the annular flangedefining an interior cavity configured to receive the spring.
 7. Thecatheter of claim 6, wherein the spring comprises at least one memberthat is biased radially outward.
 8. The catheter of claim 7, wherein thespring comprises a pair of annular rings having the plurality ofleaflets extending between the pair of annular rings.
 9. The catheter ofclaim 7, wherein the spring comprises an annular ring having a pluralityof tabs extending proximally from the annular ring.
 10. The catheter ofclaim 5, wherein the spring comprises nitinol.
 12. The catheter of claim5, wherein the spring is over-molded within an outer periphery of theproximal portion.
 13. The catheter of claim 1, wherein the distalportion is conical.
 14. The catheter of claim 1, wherein the outerprofile of the proximal portion is arcuate.
 15. The catheter of claim 1,wherein the outer profile of the proximal portion is tapered.
 16. Amethod of implanting a prosthesis, the method comprising: inserting aretaining sleeve and a distal tip assembly of a catheter assembly into abody lumen, the retaining sleeve being positioned over the prosthesis,the retaining sleeve having an outer diameter, the distal tip assemblyhaving a distal portion and a proximal portion; expanding an outerdiameter of the proximal portion of the distal tip assembly such thatthe outer diameter of the proximal portion is larger than the outerdiameter of the retaining sleeve.
 17. The method of claim 16 furthercomprising advancing the distal tip assembly and the retaining sleevethrough a body lumen to an implementation site.
 18. The method of claim16, wherein the prosthesis is a valve prosthesis for implantation withinthe heart.
 19. The method of claim 16, wherein the proximal portioncomprises a balloon element that forms a cavity, and wherein expandingthe outer diameter of the proximal portion of the distal tip assemblycomprises increasing a pressure within the cavity formed by the balloonelement.
 20. The method of claim 16, wherein the proximal portion of thedistal tip assembly comprises a biasing member, and wherein expandingthe outer diameter of the proximal portion of the distal tip assemblycomprises passing the proximal portion past a distal end of anintroducer such that the biasing member expands the proximal portion.